1. Field of the Invention
The present invention relates to an improvement in a vapor deposition film forming apparatus, and more particularly to an improvement in an apparatus for forming a photo-conductive film, a semiconductor film, an inorganic insulative film or an organic resin film on a conductive substrate by a plasma CVD method.
2. Description of the Prior Art
In a prior art apparatus for forming an electrophotographic photo-conductive drum by depositing an amorphous silicon photo-conductive film on a cylindrical metal substrate surface such as an aluminum surface by a plasma CVD method, a cylindrical cathode electrode which is coaxial with the substrate is arranged so that a glow discharge occurs between the electrode and the substrate. An example of such an apparatus is shown in FIG. 1 in a longitudinal sectional view. Numeral 11 denotes a cylindrical cathode electrode which is coaxial with a cylindrical substrate (anode electrode) 12. Numeral 13 denotes a doughnut-shaped electrical insulator, numeral 14 denotes a vacuum chamber wall, numeral 15 denotes an RF power supply, numeral 16 denotes a reaction gas discharge pipe, numeral 17 denotes a vacuum exhaust pipe, numeral 18 denotes a substrate heater, numeral 19 denotes a substrate rotating mechanism and numeral 20 denotes ground.
In this apparatus, since one substrate is arranged in one reactor, distribution of thickness of the amorphous silicon film which is easily affected by a gas flow path can be readily adjusted, and an excellent film characteristic is obtained because of excellent discharge stability.
In a mass-production by such an apparatus, it is necessary to increase the number of reactors. It is usually required for independent control of discharge parameter to provide a reaction gas supply system, a vacuum exhaust system and an RF power supply separately for each reactor. FIG. 2 shows a diagram of a multi-reactor apparatus in which four reactors are used. Numeral 1 denotes a reactor, numeral 2 denotes a matching circuit, numeral 3 denotes an RF power supply, numeral 4 denotes a coaxial cable, numeral 5 denotes a vacuum pump, numeral 6 denotes an exhaust pipe, numeral 7 denotes a reaction gas flow rate controller and numeral 8 denotes a reaction gas supply pipe.
As the number of reactors increases as shown in FIG. 2, associated facilities also increase proportionally and the parameters must be controlled for each reactor. Thus, in the prior art apparatus, it has been inevitable that the increase of the number of reactors increased the associated facilities and complicated the control operation.
When a number of deposition films are to be formed, if the RF power supply, matching circuit and coaxial cable are separately arranged for each reactor as was done in the prior art apparatus, the discharge parameters can be independently controlled but impedance matching should be individually adjusted and it is difficult to form the deposition films with the same condition in the respective reactors.
Further, the more the deposition films to be formed are, the more are the reactors as well as the RF power supply system facilities including the RF power supplies for supplying RF powers to the reactors and the matching circuits for matching the impedances of the RF glow discharges required.